The present invention relates to a multi-channel sound transmission method and more particularly to a multi-channel sound transmission method with stabilization of phantom sound sources.
Conventional multi-channel sound transmission methods, such as the quadrophony method and the 3/2-or Dolby pro logic method, use various matrix codings with different directional resolutions to the front. For the most part, these methods provide for using a central loudspeaker, which, however, often has a disturbing effect with regard to an accompanying image. Also, when there is no central loudspeaker, a lack of center orientation can be detected, which has quite a disadvantageous effect. Moreover, the ambient background sound often seems detached from the zone that determines the direction to the front, and it is difficult to realize desired lateral or side sources. The phantom sound sources between the loudspeakers are relatively unstable due to the frequency response characteristic, signal coherence, and listener position. An overview of the multichannel sound system theory is described, for example, in issues 4 and 5/93, pp. 24 to 32, or 47 to 48 by R. Schneider in Production Partner, which is herewith incorporated by reference herein.
In conventional, auralization methods, spatial pulse responses are obtained in real or computer-simulated rooms, which after being convolved with a dry sound signal, usually by way of binaural headphone reproduction, less often by way of a multi-channel loudspeaker reproduction, render possible an enveloping sound reproduction. A disadvantage of these methods is that the only reproduction possible is that of a point source that can be localized. Moreover, in another conventional method by means of four microphones, three having a bilateral or octogonal characteristic and one having an omnidirectional characteristic, a previously recorded space is realized using a matrix circuit. However, the resolution is relatively low. Auralization methods are described, for example, in the essay, xe2x80x9cAuralizationxe2x80x94An Overviewxe2x80x9d by Kleiner, M.; Dalenbxc3xa4ck, B.-I.; Svensson, P. in JAES, vol. 41, no. 11 (1993) pp. 861-875, which is hereby incorporated by reference herein.
In xe2x80x9cNew Method for Sound Reproduction,xe2x80x9d IEEE Transactions on Consumer Electronics, Vol. 35, No. 4, November 1989, the contents of which are hereby incorporated by reference herein, a single pulse sound is used to measure reflections. The reproduced sound field can then be calculated through convolution of two kinds of reflections. This method has the disadvantage that phantom sound sources cannot be stabilized and that different listening areas can be realized.
An object of the present invention is to improve upon the stability of the phantom sound sources and to prevent, to the greatest extent possible, the reproduced sound from coinciding with the most proximate loudspeaker.
Another object of the present invention is to create a multi-channel transmission method which will make it possible to prevent phantom sound sources from wandering in an unintended manner, and which will ensure that for listener locations, which are not situated exactly in the middle of the axis between two loudspeakers, the localization of the sound source will fall in the most proximate loudspeaker.
The method of the present invention and achievement thereof are characterized, in particular, that with the aid of a multi-channel spatial pulse reception, at least two excitation locations and at least two-times three closely proximate microphone locations are used for one or more variably oriented directional microphone(s) in a real or simulated room for receiving the spatial pulse responses, a convolution processing takes place with a plurality of directly received sound signals, conforming at least in number to the spatial pulse responses, in digital sound-processing processors (5) and, in fact, so that the convolved signals are locally distributed between, or in a borderline case, at the locations of the reproduction loudspeakers or at the boundaries of a binaural signal, when the sound is reproduced via headphones.
Other farther features or embodiments of the present invention include: (a) that to receive the spatial pulse responses in a simulated room, counting segments to this effect are used (see block 108 of FIG. 4); (b) for the spatial sound transmission, a directional microphone (1) or a plurality of directional microphones (1, 2) or counting segments for receiving the pulse-response measuring signals radiated from at least two excitation locations, e.g., loudspeakers, is swivelled around the center point of the pick-up location, and at least three reproduction loudspeakers (4 and 6) of the sound signals convolved by the digital sound-processing processors (5) are oriented in the opposite direction to the orientation of the microphones or of the counting segments to detect the spatial pulse response; (c) to move phantom sound sources within the area of the first reflections of the spatial pulse responses between two values determined by interpolation (see block 110 of FIG. 4), a continuous transition takes place; (d) for use for a large-picture video conference, a locally separated three-channel transmission via two loudspeakers arranged to the left and right of the video screen, three spatial pulse responses from three side-by-side source locations are detected, which are used for purposes of convolution processing with the three dry sound signals from the right, middle, and left speakers being reproduced on the video screen, and that when the convolved sound signals are reproduced, the convolved sound signals originating from the right sources are reproduced via the right loudspeakers; those originating from the left sources via the left loudspeaker, and those convolved sound signals originating from the middle sources are reproduced with equal intensity via the two loudspeakers; and (e) to obtain an identically sounding reproduction from all three identically sounding source groups in (d), the middle group radiated from the two loudspeakers is reproduced, for example, at a level diminished by three dB compared to the two lateral source groups.
The present method makes it possible, inter alia, for relatively large listening surface areas to be produced, which under known stereophonic methods had often made up just one narrow area. This is achieved by performing an auralization, where conditions are improved by prompting a plurality of spatial pulse responses from various locations in the same room, to be received via a multi-channel receiving apparatus, for example, a directional microphone, at one location, and to be recorded. A multi-channel loudspeaker arrangement is used for the reproduction. The stability of the phantom sound sources is also improved, in particular, and the reproduction is largely prevented from coinciding with the most proximate loudspeaker.